Obtaining pressure of an operating environment of a bi-directionally scanning electrophotographic device for implementing corrections per pressure

ABSTRACT

Methods and apparatus include improving print quality of a bi-directionally scanning electrophotographic (EP) device, such as a laser printer or copy machine, according to ambient pressure in which operated. A moving galvanometer or oscillator reflects a laser beam to create scan lines of a latent image in opposite directions. A damping of the motion occurs per air density implicated by temperature and pressure, where the pressure changes occurring especially from altitude changes. During use, a drive signal, such as a pulse train, moves the galvanometer or oscillator at or near its resonant frequency. Based on a parameter of the drive signal, such as pulse width, the ambient pressure can be made known. In general, a high-pressure environment requires a relatively longer pulse width to resonate the galvanometer or oscillator in comparison to a shorter pulse width for a low-pressure environment. Corrections to print quality stem from the determined ambient pressure.

CROSS REFERENCE TO RELATED APPLICATION

Pursuant to 37 C.F.R. §1.78, this application is a divisional and claimsthe benefit of the earlier filing date of application Ser. No.12/858,574, filed Aug. 18, 2010, entitled “Obtaining Pressure of anOperating Environment of a Bidirectionally Scanning ElectrophotographicDevice for Implementing Corrections per Pressure,” which is itself adivisional application claiming the benefit of the earlier filing dateof application Ser. No. 11/513,951, filed Aug. 31, 2006, entitled“Obtaining Pressure of an Operating Environment of a BidirectionallyScanning Electrophotographic Device for Implementing Corrections perPressure.”

FIELD OF THE INVENTION

Generally, the present invention relates to electrophotographic (EP)devices, such as laser printers or copy machines. Particularly, itrelates to improving print quality in electrophotographic devicesutilizing bidirectional scanning. In one aspect, EP devices arecharacterized according to pressure. In another, ambient operatingconditions are obtained and corrections implemented. In still otheraspects, pressure is obtained from understanding movement of structuresin the EP device that are influenced by pressure.

BACKGROUND OF THE INVENTION

Traditional electrophotographic (EP) devices have a spinning polygonmirror that directs a laser beam to a photoconductor, such as a drum, tocreate one or more scan lines of a latent to-be-printed image. Recently,however, it has been suggested that torsion oscillator or resonantgalvanometer structures can replace the traditional spinning polygonmirror and create scan lines in both the forward and reverse directions(e.g., bi-directionally), thereby increasing efficiency of the EPdevice. Because of their MEMS scale size and fabrication techniques, thestructures are also fairly suggested to reduce the relative cost ofmanufacturing. Unfortunately, scanning in two directions adds a measureof complexity to image referencing since reference points need occur foreach of the forward and reverse scans at opposite ends of the printedpage and the slightest of deviations amplifies print imageimperfections. Also, any asymmetry in the motion of the oscillator orgalvanometer results in errors in print linearity and line-to-lineregistration across the printing area.

Under ideal conditions, the oscillator or galvanometer is wellcontrolled by a drive configuration to move it sinusoidally withoutimpedance. Because of modern design constraints, however, sinusoidaldrives are somewhat impractical or economically infeasible. In turn,more practical drive configurations consist of a sequence of pulses,each of which causes a corresponding force to be imparted to thegalvanometer or oscillator to make it move. Problematically, there is anotable drawback in the discontinuous nature by which forces are appliedto the galvanometer or oscillator and asymmetric distortion of laserscanning motion can be introduced if left uncontrolled.

Since the mechanical properties of the constituent materials thatcompose the galvanometer or oscillator are influenced by temperature,and the damping of the motion is dependent on air density (in turn, aresult of both temperature and pressure, where pressure varies withaltitude, for instance), it is clear that ambient operating conditionsaffect the shape and magnitude of the linearity and misalignment of scanlines. In this regard, print quality changes occur as a result ofchanges in operating altitude, temperature or from large barometricchanges, for example. While electronic measurement of temperature can beimplemented with relatively simple and low cost components, measurementof pressure generally cannot, and introducing relatively high costcomponents to compensate for nonlinearity and misalignment would negateany prospective cost savings from using the galvanometer or oscillator.

Accordingly, there exists a need in the art for characterizing themanner in which bi-directionally scanning EP devices should operateaccording to various operating conditions, especially pressure.Particularly, there are needs by which knowing the actual operatingconditions of the EP device will relate to making corrections to improveprint quality. Ultimately, the need extends to simply and efficaciouslyobtaining pressure without introducing high-cost components. Naturally,any improvements should further contemplate good engineering practices,such as relative inexpensiveness, stability, low complexity, ease ofimplementation, etc.

SUMMARY OF THE INVENTION

The above-mentioned and other problems become solved by applying theprinciples and teachings associated with the hereinafter describedobtaining pressure of operating environments of bi-directionallyscanning electrophotographic (EP) devices, such as laser printers orcopier machines, so that corrections can be implemented. In a most basicsense, an EP device is pre-characterized such that pressure iscorrelated to expected positional misalignment of scan lines. Based uponattainment of actual ambient operating conditions, the EP device underconsideration is corrected to prevent or otherwise overcome the expectedpositional misalignment.

In this regard, an EP device includes a scanning mechanism in the formof a moving galvanometer or oscillator that reflects a laser beam tocreate scan lines of a latent image in opposite directions. A damping ofthe motion of the galvanometer or oscillator occurs per operatingconditions, such as air density implicated by temperature and pressure(the pressure changes occurring especially from changes in altitude). Toobtain pressure, a drive signal, such as a sequence of pulses, moves thegalvanometer or oscillator at its resonant frequency. Based upon aparameter of the drive signal, such as pulse width, the ambient pressurecan be made known. For instance, an EP device operated in a relativelyhigh-pressure environment requires a relatively longer pulse width todrive the galvanometer or oscillator at its resonant frequency with aspecified amplitude, whereas a shorter pulse width is required for arelatively low-pressure environment. In turn, the relationship can bemapped and stored. Corrections to improve print quality then occuraccording to the determined ambient pressure. Certain correctionsinclude producing the latent image with a signal altered from an imagedata input signal.

These and other embodiments, aspects, advantages, and features of thepresent invention will be set forth in the description which follows,and in part will become apparent to those of ordinary skill in the artby reference to the following description of the invention andreferenced drawings or by practice of the invention. The aspects,advantages, and features of the invention are realized and attained bymeans of the instrumentalities, procedures, and combinationsparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of thespecification, illustrate several aspects of the present invention, andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a diagrammatic view in accordance with the present inventionof a representative bi-directionally scanning EP device;

FIGS. 2A-2D are diagrammatic views in accordance with the presentinvention of desirable scan lines and reference positions in abi-directionally scanning EP device and representative potential scanmisalignments of same;

FIG. 3 is a diagrammatic view in accordance with the present inventionof a more detailed version of a scanning mechanism of the EP device ofFIG. 1;

FIG. 4 is a graph in accordance with the present invention of angularscan position and pulsed drive signals for the scanning mechanism;

FIG. 5 is a diagrammatic view in accordance with the present inventionof a representative distortion of a laser spot potentially occurring inthe EP device of FIG. 1;

FIGS. 6A and 6B are graphs in accordance with the present invention ofempirical and theoretic misalignment data representative of potentialmisalignments in a bi-directionally scanning EP device;

FIG. 7 is a graph in accordance with the present invention of empiricalmisalignment as a function of various pressures;

FIG. 8 is a surface plot in accordance with the present invention of arepresentative model pre-characterizing an EP device according topressure and temperature;

FIG. 9 is a graph in accordance with the present invention of maximummisalignment as a function of pressure change relative to a basepressure;

FIG. 10 is a graph in accordance with the present invention of maximummisalignment as a function of pulse width for driving a scanningmechanism at resonance;

FIG. 11 is a graph in accordance with the present invention ofmisalignment as a function of time for scanning; and

FIG. 12 is a graph in accordance with the present invention of a driveparameter for driving a scanning mechanism at resonance as a function ofpressure change relative to a base pressure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

In the following detailed description of the illustrated embodiments,reference is made to the accompanying drawings that form a part hereof,and in which is shown by way of illustration, specific embodiments inwhich the invention may be practiced. These embodiments are described insufficient detail to enable those skilled in the art to practice theinvention and like numerals represent like details in the variousfigures. Also, it is to be understood that other embodiments may beutilized and that process, mechanical, electrical, software, and/orother changes may be made without departing from the scope of thepresent invention. In accordance with the present invention, theobtaining of pressure of an operating environment of a bi-directionallyscanning electrophotographic (EP) device, so that corrections perambient pressure can be implemented, is hereafter described.

With reference to FIG. 1, an EP device 20 of the inventionrepresentatively includes mono or color laser printers or copiermachines. During use, image data 22 is supplied to the EP device fromsomewhere external, such as from an attendant computer, camera, scanner,PDA, laptop, etc. A controller 24 receives the image data at an input 26and configures an appropriate output, video signal 28 to produce alatent image of the image data. In turn, a hard-copy printed image 29 ofthe image data is obtained from the latent image. If print alignment andoperating conditions of the EP device are well calibrated, the printedimage 29 corresponds nearly exactly with the image data input 22. Ifnot, the printed image has poor quality, especially in the form of avariety of misalignments.

With more specificity, the output, video signal 28 energizes a laser 30to produce a beam 32 directed at a scanning mechanism 39, such as atorsion oscillator or resonant galvanometer. As the oscillator orgalvanometer moves (indicated by oscillation wave lines 136) the beam 32is reflectively cast to create beam lines 34 a, 34 b on either side of acentral position 34. As a result, multiple scan lines in alternatedirections are formed on a photoconductor 36, such as a drum, andtogether represent a latent image 38 of the image data supplied to thecontroller. Optically, certain lenses, mirrors or other structures 40exist intermediate to the photoconductor to transform the rotationalscan of the laser beam reflected from the oscillator or galvanometer 39into a substantially linear scan of the beam at the photoconductor 36,with substantially uniform linear scan velocity and with substantiallyuniform laser beam spot size along the imaging area of the drum. Toprovide common reference for the beam lines, various sensors areemployed. Preferably, a forward sensor 42 a and a reverse sensor 42 b,called horizontal synchronization (hsync) sensors are positioned nearopposite ends of the photoconductor to provide a common reference forall forward scanning beam lines and all reverse scanning beam lines,respectively. In addition to, or in lieu of the sensors 42 a, 42 b,forward and reverse hsync sensors may be positioned at 44 a and 44 b,upstream of the representative optics 40. Alternatively still, a singlehsync sensor might be used with one or more mirrors emplaced variouslyto act as a second hsync sensor. Regardless, the outputs of thesesensors (representatively given as line 43 from hsync sensor 42 a) aresupplied to the controller 24 for referencing correct locations of thescan line(s) of the latent images. Downstream of the latent image, andnot shown, the printed image is formed by applying toner to the latentimage and transferring it to a media, such as a sheet of paper.Thereafter, the media 45 with the printed image 29 exits the EP device,where users handle it for a variety of reasons.

Unfortunately, the printed image 29 is not always an accuraterepresentation of the image data input 22 and various operations areemployed to tightly calibrate the EP device. In this regard, atemperature and pressure sensor 47 and 49 are provided to supply inputto the controller to correct the EP device per ambient operatingconditions, such as pressure and temperature. A controller function oralgorithm A then uses the obtained pressure and temperature to implementa correction in the output, video signal 28 from the supplied image datainput signal at 26. In placement, the sensors can typify any locationinternal or external to the EP device although both are shown generallynearby the controller, within a housing 21. However, a more likelyposition for the temperature sensor 47 is that of nearby the laser beam30 at position 48, for instance, to better ascertain the temperature ofthe structures that actually form the scan lines of the latent image. Asa corollary, a more likely position of the pressure sensor is that ofrelatively far away from any moving structures able to influenceairflow, such as at position 49, so that pressure readings are notunduly influenced by fluctuating air. In form, the temperature sensormay representatively embody items such as a temperature sense resistor,a thermocouple, a thermistor, or any other detector influenced bythermal variations. Pressure sensors, on the other hand, mayrepresentatively embody items such as a diaphragm, a transducer, acapacitor, or any other detector influenced by pressure variations. Toavoid relative cost, the pressure may be also inferred from othercomponents of the EP device, as will be described in detail below,without need of taking direct pressure readings from sensor 49.

Before then, however, FIG. 2A conceptually shows the desired scan linesand reference positions in a bi-directionally scanning EP device andfairly suggests the nomenclature for use with later figures. Namely, aplurality of scan lines forming a latent image on a photoconductor, forexample, are sequentially numbered 1-6, with odd numbered scan lines (1,3, and 5) occurring in a forward scan direction 52 a opposite the evennumbered scan lines (2, 4, and 6) occurring in a reverse scan direction52 b. Also, the forward and reverse scan lines alternate with oneanother and such is the nature of scanning with the torsion oscillatoror resonant galvanometer and its attendant formation of forward-scanningbeam lines 34 a and reverse-scanning beam lines 34 b. Also, thereference position 54 a supplies a common reference point for each ofthe forward scanning lines and is borne about by the signal from theforward hsync sensor. Conversely, the reference position 54 b supplies acommon reference point for each of the backward scanning lines and isborne about by the signal from the reverse hsync sensor.

In FIGS. 2B-2D, the potential misalignments of bi-directional scans inan EP device may be classified into three basic categories. In the first(FIG. 2B), the end points 56′, 58′ of forward (fwd) scan lines 56, 58 donot coincide with the start points 57′, 59′ of reverse (rev) scan lines57, 59 and is known herein as straight bi-directional misalignment. Thescan lines are all also of relatively equal length thereby creating anearly equal amount 60 of misplacement at each end of the scans. In thesecond (FIG. 2C), line length mismatch occurs. That is, the forward andbackward scan lines are aligned on one side 62, but not on the otherside where an amount 63 of mismatch occurs. In a typical embodiment,this is the result of forward and reverse scan lines having differinglengths. In the third (FIG. 2D), differential nonlinearity is observed.Namely, printed pels (pel #1-pel #n) within each forward or reverse scanare normally intended to be equally spaced apart. However, if there aredifferences in the linearity of pel placement between forward andreverse scans, there will be individual shifts 65 in the placement ofsets of pels that occur in the same scan location among scans as shown.To the extent misalignment occurs in an actual bi-directionally scanningEP device, skilled artisans will appreciate that most misalignments takethe form of some combination of more than one of the foregoing types. Tothis end, ambient operating conditions, especially pressure, areascertained to help implement corrections.

With reference to FIG. 3, a slightly more detailed version of thescanning mechanism 39, such as a galvanometer or oscillator, of the EPdevice is shown. In this regard, the scanning mechanism includes areflective surface 35, such as a mirror, that is caused to rotate abouta central pivot point in either a first direction given by arrow A or inan opposite direction given by arrow B. The laser beam 32 upon hittingthe reflective surface is then caused to impinge upon the photoconductor36 to make scan lines of a latent image in opposite directions given bybi-directional arrow C. Also, drive means (not shown) exert a torque onthe scanning mechanism to push it, so to speak, to rotate (in either thedirection of arrow A or B). In this regard, the torque occurs for arelatively short period of time, but adds a sufficient amount of energyto the system of the scanning mechanism so that correct scan amplitudeis maintained for at least both a right half of a forward scan and aright half of a scan in the reverse. Thereafter, upon the scanningmechanism reaching a corresponding mid-point or centerline of its scanline, the scanning mechanism is similarly pushed (now in the oppositedirection of either arrow A or B) to complete the left half of thereverse scan line, followed by the left half of the forward scan line.Over time, the process repeats and multiple scan lines are produced. Byanalogy, the scanning mechanism is akin to a pendulum that gets pushedin both a forward and reverse direction. By operation of gravity andother forces, the pendulum reverses direction on its own as ittransitions from the forward to the reverse directions at the apex. Tokeep the pendulum swinging with a desired amplitude, pushes areoccasionally given. Diagrammatically, the halves of the scan lines areseen in FIG. 2 according to the right half RH and left half LH appearingon opposite sides of a centerline CL. It is also the case that thehighest drive efficiency is achieved when the frequency of the push ofthe scanning mechanism (or pendulum, by analogy) coincides with theresonant frequency of the scanning mechanism.

With reference to FIG. 4, assuming that the optics are designed toappropriately transform the nonlinear angular motion of the laser beamreflected from the mechanism into linear motion of the laser spot on aphotoconductor, the ideal motion of the mechanism driven by anappropriate electronic driver is described by the sinusoidal equation:θ(t)=A·sin(ω·t)  Equation 1;where θ(t) is the instantaneous angular position of the mechanism, withθ=0 occurring at the centerline (CL, FIG. 2) of the scan, A being themaximum excursion of the beam, ω being the radian frequency of themotion, and t being the time. Akin to the pendulum analogy, the drivercontrols the amplitude and frequency of the motion, but the mostefficient operation occurs if the scanning mechanism is driven or pushedat or near its natural resonance point. While the actual motion of thelaser spot is affected by several factors, including for example, (1)the drive method and configuration of the scanning mechanism, (2)nonlinear damping of the scanning mechanism, (3) misalignment of thescanning mechanism, and (4) nonlinearity of various optics in the EPdevice (such as element 40), near-ideal motion can be obtained if thedrive mechanism could, indeed, follow the θ(t) curve. As before,however, design constraints generally make such impractical oreconomically unfavorable.

Thus, the more practical drive approach is shown via a sequence ofpulses P, each of which causes a corresponding force to be imparted tothe scanning mechanism to make it resonate at its resonant frequency.Such also occurs by imparting an electromagnetic, electrostatic or otherforce and coupling it to the scanning mechanism via an appropriatelypositioned electromagnetic, electrostatic, or other coupling receiver(not shown). While the amplitude of the pulses is fixed, the duration pwof each pulse can be dynamically varied to maintain consistent scantimes as measured by optical sensors, (e.g., hsync sensors) according tothe shown time t, which intercept the scanning laser beam on either endof the scan lines. In general, the greater the air resistance in theoperating environment, the wider or longer the pulse width that isrequired. Conversely, the lesser the air resistance in the operatingenvironment, the shorter the pulse width that is required. Regardless,both the lengthening and shortening of the pulse width occurs via afeedback drive scheme. This drive scheme is also particularly wellsuited to a controller 24 of FIG. 1 contemplative of a digital controlsystem in which a digital controller (e.g. microcontroller,microprocessor, DSP, ASIC, or FPGA) is designed to provide pulses ofprecise duration and timing to the scanning mechanism, such as alongcontrol line 23, and to accurately measure the timing of feedbacksignals, e.g., line 43, from the sensors. Also, while measuring thedifference between the times that the laser beam strikes a first sensorat one end of the photoconductor to the time that it strikes a secondsensor at the opposite end, the controller can maintain a constant laserbeam transit time across the printing area by varying the width of eachof the drive pulses. A procedure can then be used to locate the preciseresonance frequency by stepping through a range of frequencies anddetermining which frequency results in the narrowest or shortest pulsewidths.

In other words, under normal resonant operation of a scanning mechanism,the width of the pulses required to properly drive the mechanism willvary as a function of the device efficiency and environmental factors,including temperature and pressure. For example, as air pressuredecreases as a result of changes in altitude, the density of the airwill decrease, and therefore the amount of damping presented to themechanism will likewise decrease as a result of reduced air resistance.It will therefore require less energy, and correspondingly shorter drivepulses to maintain the same scan transit time.

In this regard, a variable (“PI_Total”) can be defined to represent theinstantaneous strength of the drive signal. Namely, this variable isdefined as the difference between the current width of the pulse (pw),in the actual operating environment to resonate the scanning mechanismat the required amplitude, and some nominal pulse width value. In turn,the nominal value is specific to a particular EP device and isdetermined by measuring the pulse width necessary to resonate thescanning mechanism under a standard set of operating conditions, or itmay be representative of a particular EP device design, determinedeither theoretically or through collection and processing of data on astatistical sample of units, or both. Relative to operating conditions,the ambient air pressure is related to the variable PI_Total, since thestrength of the drive signal (e.g., pulse train) is directly dependentupon the amount of damping presented to the device, which is in turndependent upon air pressure. As in FIG. 12, described below, thisrelationship is evident in both theoretical and empirical modeling.

With reference to FIG. 5, a drive pulse P for pushing a scanningmechanism is shown relative to how desired and undesired pixels (pels)occur on adjacent forward and reverse scan lines in a portion of theprinting area 60. White circles 62 indicate ideal or desired pellocations, while solid or darkened circles 64 indicate actually printedpel locations. During use, when the drive pulse P is applied, there is asmall deviation from the ideal scan. Damping caused primarily by airresistance slows the scanning mechanism as it moves through one halfcycle (e.g., a right half RH of the printing area 60 relative to thecenterline CL), which in turn causes successive pels to lag(alternatively, lead—not shown) in the direction of travel, resulting inprint nonlinearity. The amount of deviation between the ideal and actualpel locations, e.g., circles 62 compared to circles 64, respectively,increases over time as the effect of the applied force is damped. Forinstance, as the scanning mechanism creates a scan line in the forwarddirection toward the right half RH of the printing area 60 relative tothe centerline CL, the darkened circle 64 and the underlying whitecircle 62 align and register fairly well at a position 68 near thecenterline. As travel of the scan line progresses, however, thealignment and registration of the white and darkened circles varies,such as at position 69, such that the ideal and the actual pels do notalign perfectly. Continuing, the scan line reverses course from aforward direction 52 a to a reverse direction 52 b, according to therepresentative arrow D, and alignment and registration of the ideal andactual pels separates even further, such as at position 70. Ultimately,the mismatch between the ideal and actual is greatest near thecenterline CL, such as near position 72, before scanning in the reversedirection occurs in the direction 52 b for the left half LH of theprinting area 60. As is then seen, the resulting linearity error variesacross the scan lines, with the maximum error occurring at or near thecenterline CL position at which the drive pulses occur. Moreover,non-linearity produced in reverse scan lines is opposite in direction tothat produced in forward scan lines, and therefore, a misalignmentbetween pels on adjacent scan lines will occur with a maximum alignmenterror of double the linearity error.

Plotting this out, FIGS. 6A and 6B show empirical and theoreticalresults, respectively, resembling a “V” shaped curve 80 and 80′. In FIG.6A, numerous sample points were obtained in creating curve 80 for an EPdevice and skilled artisans will observe that the closer the scan lineis to the centerline, the worse the misalignment between the ideal andthe actual pel locations. Because only actual pels can be measuredrelative to other pels, and not ideal pels relative to actual pels, thegraph more precisely represents distances of misalignment relative toadjacent pels, and adjacent pels in adjacent scan lines (forward versusreverse scan line, and vice versa). Correlating back to FIG. 5, adistance d1 exists of about 175 microns between adjacent darkenedcircles 64-a and 64-b near the centerline CL. Further away from thecenterline CL, however, the distance between pels is much closertogether. In other words, the misalignment is less at distance d2between adjacent darkened circles 64-c and 64-d compared to distance d1.Skilled artisans will also note that the horizontal position on thegraph (x-axis) extends to about +/−100 mm in length. By converting toinches, a media of about 8.5 inches wide by 11 inches long has about+/−108 mm per each left and right half LH, RH of the 8.5 inches relativeto centerline and a few millimeters per the 8.5 inch-wide media isunused. That is, about 8 mm per each of the left and right halves of themedia are not printed on and, thus, has no misalignment and theempirical data only covers the +/−100 mm.

In FIG. 6B, it is shown that the theoretical curve 80′ of misalignmentcorroborates the empirical curve 80 of misalignment, with the greatestamount of misalignment occurring near the centerline. It also indicatesthat a scanning mechanism exhibits somewhat distorted misalignment nearthe centerline, at position 85 for instance, from a pulse train whosefrequency does not match the resonant frequency of the scanningmechanism, thereby creating a phase shift between the drive pulse trainand the scanning motion of the scanning mechanism.

With reference to FIG. 7, a plurality of superimposed curves are givenshowing empirical or measured misalignment profiles changed as afunction of relative air pressure reduction, which certainly occurs as aresult of changes in altitude of the operating environment. In thisregard, a baseline plot 95 is given for a standard operating pressure,such as at 29.92 inches of mercury (Hg). Thereafter, the plots are givenrelative to the baseline in millimeters of mercury (Hg). As is apparent,the misalignment improves with lower pressure, or at higher altitude,such is given by plot 97. Correspondingly, the steepness of the V-shapedprofile will flatten-out or “steepen-up” as will the legs 103, 104 ofthe profile have a variable amount of slope, as will be better definedbelow. Relative to temperature changes, the V-shaped plots would eitherrise or lower from, for example, having an apex 99 to either having anapex at position 101 or having an apex at 102, respectively, astemperature increased or decreased, respectively.

Accordingly, the inventors have empirically and theoretically shown thatmisalignment gets better or worse according to various pressures andtemperatures of an operating environment in which a mechanical structureof a bi-directionally scanning EP device is operated to create scanlines. With reference to FIG. 8, modeling or pre-characterizing thisresults in a set of surface plots, such as 110, giving parameters to afunction describing the amount of error at each position on the page.Alternatively, the model could be expressed in forms such as functional,tabular, or algorithmic data, or a combination thereof so long asrelationships between the measured or obtained independent variables(scan position, temperature, and pressure) and a dependent variable ofinterest (forward-reverse alignment error or linearity error) are known.Moreover, the model may be based on empirical measured data, ontheoretical physical principles, or on a combination thereof.

As a working example of the model, consider the operating point shown.If it was ascertained that the temperature of the EP device was 23.4degrees Celsius, and the pressure (relative to some baseline, as before)was −123, a slope amount m of about 1.6 could be ascertained. Relativeto other models (not shown, but plotted representatively the same), atemperature and pressure entry point would also reveal a correspondingparameter of b (y-intercept of the V-shaped curve) and an “a” valuecorresponding to how sharp a transition the V-shaped curve makes (a high“a” value is a very pointy V-shape whereas a low “a” value is a morerounded V-shape at the apex).

In turn, plugging the obtained or ascertained variables (m, b and a)into an equation defining the V-shaped curves of FIGS. 6A and 6B, forinstance, the amount of misalignment in a bi-directionally scanning EPdevice can be known. Representatively, the following equation has beenobserved to fairly well define the V-shape of the data and plugging theobtained variables (m, b and a) into it reveals a fair approximation ofthe amount of misalignment in an EP device.y(x)=[((2^((ax))−1)mx)/(2^((ax))+1))+b]  Equation 2;

where x is the relative horizontal position, e.g., the x-axis aspreviously shown. In turn, knowing the amount of misalignment per anoperating condition of the EP device, such as pressure or temperature, askilled artisan can enter a correction to compensate for themisalignment in advance of the misalignment actually occurring in aprinted image. Skilled artisans will also know how to correlate orconvert the amount of misalignment (e.g., a first distance) to: 1) imagedata input, especially in the form of pixels (pels) of a fixed length(e.g., a second distance), such as 600 or 1200 dots per inch (dpi); or2) pulse widths pw, so that the pixel information for scanning a latentimage on a photoconductor is readily also known according to pressureand/or temperature (and a correction readily implemented).

For instance, FIG. 9 shows a curve 100 correlating the amount of maximumoffset (e.g., the apex of the V-shaped curve) relative to air pressure.In that pressure is again relative to a baseline pressure, e.g., the 0point, the other pressures are given as negative numbers in millimetersof mercury. In FIG. 10, curve 110 shows this same amount of maximumoffset (alternatively stated as a central deviation) relative to thepulse width of one or more pulses of a pulse train to drive the scanningmechanism at resonance. In FIG. 11, a curve 120 representatively shows aforward to reverse scan line offset relative to scan times. It alsosuperimposes various pressures with the bottom curve 122 being thebaseline pressure with the top curve 124 being the lowest pressure.

Lastly, FIG. 12 shows the previously discussed PI_Total relative topressure as pluralities of curves 130 empirically measured for pluralityof individual EP devices, such as those with names or identifiers Hn 27,28, 45 and 52. As is apparent, each is a straight line. It is also thesituation that PI_Total equals the pulse width pw of a presentlymeasured pulse of a train of pulses (e.g., FIG. 4) to resonate thescanning mechanism under ambient operating conditions minus a pulsewidth of a nominal pulse, as before. Thus, by rearranging the PI_Totalequation, a pulse width pw of a presently measured pulse of a train ofpulses to resonate the scanning mechanism under ambient operatingconditions is known directly relative to pressure (or the vacuum axis inmillimeters of mercury as shown). As a result, pressure need not beactually measured in an EP device and can be obtained by simply knowingthe actual pulse width pw necessary to drive a scanning mechanism atresonant frequency under ambient operating conditions. In this manner,expensive pressure sensor components in manufacturing an EP device, forinstance, can be avoided. Pressure can also be updated whenever desiredsimply by having the controller or other function ascertain the pulsewidth of the pulses required to drive the scanning mechanism at itsresonant frequency at an appropriate amplitude. In other words, a realtime pressure sensor is made available. Naturally, alternate embodimentscontemplate ascertaining other parameters of a drive signal of ascanning mechanism at resonance, other than just a pulse width of apulse train.

One of ordinary skill in the art will recognize that additionalembodiments of the invention are also possible without departing fromthe teachings herein. This detailed description, and particularly thespecific details of the exemplary embodiments, is given primarily forclarity of understanding, and no unnecessary limitations are to beimported, for modifications will become obvious to those skilled in theart upon reading this disclosure and may be made without departing fromthe spirit or scope of the invention. Relatively apparent modifications,of course, include combining the various features of one or more figureswith the features of one or more of other figures.

The invention claimed is:
 1. A method of operating a device having amoving galvanometer or oscillator, comprising: providing a drive signalto substantially resonate the galvanometer or oscillator; determining aparameter of the drive signal from which ambient pressure is to bedetermined; determining ambient pressure of the device based on theparameter of the drive signal; and implementing a correction foroperating the device based on the determined ambient pressure, whereinthe providing the drive signal further includes providing a sequence ofpulses and the determining the parameter of the drive signal furtherincludes determining a pulse width of at least one pulse of the sequenceof pulses, and wherein the determining the parameter of the drive signalfurther includes determining a difference between the pulse width of theat least one pulse and a nominal pulse width, and the determining theambient pressure comprises calculating ambient pressure from thedifference using a substantially linear relationship between pulse widthand pressure.
 2. The method of claim 1, further comprising storing inthe device data characterizing a damping of a motion of the galvanometeror oscillator relative to ambient pressure under which the galvanometeror oscillator will operate.
 3. The method of claim 1, wherein the movinggalvanometer or oscillator reflects a light beam to create scan lines ofan image in opposite directions, and the correction comprises a scanalignment correction.
 4. The method of claim 1, wherein the galvanometeror oscillator reflects at least one light beam to create scan lines ofan image and the correction comprises correcting at least one of the atleast one light beam and the drive signal based upon the determinedambient pressure.
 5. The method of claim 1, wherein determining theambient pressure comprises calculating ambient pressure from theparameter of the drive signal which resonates the galvanometer oroscillator and without use of a parameter of the drive signal whichoperates the galvanometer or oscillator out of resonance.
 6. A device,comprising: a bi-directionally moving oscillator; and a controller forcontrolling the oscillator, the controller configured to controlmovement of the oscillator with a drive signal, identify a parameter ofthe drive signal at a resonant frequency of the oscillator, use thedrive signal parameter to determine ambient pressure of the device, andmodify at least one operating characteristic of the device based on thedetermined ambient pressure, wherein the drive signal parametercorresponds to a width of at least one pulse of the drive signal, andwherein the controller determines a difference between the drive signalparameter and a nominal signal parameter value, the ambient pressurebeing based upon the difference, and the controller calculates theambient pressure from the difference using a substantially linearrelationship between pulse width and pressure.
 7. The device of claim 6,wherein the controller modifies the at least one operatingcharacteristic by implementing a correction for operating the device. 8.The device of claim 6, wherein the drive signal parameter comprises anaverage pulse width of pulses appearing in the drive signal.
 9. Thedevice of claim 6, wherein the controller determines the ambientpressure by comparing the identified drive signal parameter to apredetermined value.
 10. The device of claim 6, further comprising alight source coupled to the controller for generating at least one lightbeam, wherein the oscillator reflects the at least one light beam duringoscillation and the at least one operating characteristic comprises atleast one of the at least one light beam and the drive signal.
 11. Thedevice of claim 6, wherein the nominal signal parameter value isspecific to the device.
 12. The device of claim 6, wherein thecontroller calculates the ambient pressure from the parameter of thedrive signal which resonates the galvanometer or oscillator and withoutuse of any parameter of the drive signal which operates the galvanometeror oscillator out of resonance.